Scalable switch matrix and demodulator bank architecture for a satellite uplink receiver

ABSTRACT

A scalable switch matrix and demodulator bank architecture for a satellite payload processor wherein the demodulators are connected to the output ports of the switches as the data load on the uplink beams varies. The switch matrix includes a first switch layer for receiving the uplink transmission beams and a plurality of demodulators connected to the output parts of the first switch layer. The number of demodulators is limited by the number of active uplink sub-bands which is generally less than the number of sub-bands per beam times the number of transmission beams. Thus, only a relatively few number of demodulators are distributed among the uplink transmission beams as required. This results in a readily scalable architecture having higher demodulation utilization rates than dedicated demodulation architectures.

TECHNICAL FIELD

[0001] The present invention relates generally to switch matrices, andmore particularly, to a scalable switch matrix and demodulator bankconfiguration for a high capacity multi-beam satellite uplink receiver.

BACKGROUND OF THE INVENTION

[0002] Generally, satellite uplink receivers are typically used toreceive one or more uplink transmission beams carrying radio frequencysignals. The receivers demodulate the signals for further processing,and transmit the data to downlink modulators for transmission ondownlink beams. So far the satellites have been designed to process arelatively small number of uplink transmission beams. As a result,satellite uplink receivers generally have dedicated demodulators foreach potential uplink transmission beam.

[0003] In order to increase the capacity and reuse the uplink spectrumfrequently and efficiently, there has been growing interest indeveloping satellites capable of processing several hundred uplinkbeams. Each beam can potentially carry traffic up to the capacity of thefull uplink spectrum. However, due to limitations on frequency re-useand satellite processing power, the total footprint capacity isgenerally much less than the maximum beam capacity times the number oftransmission beams. Accordingly, in a satellite system designed toprocess, for example, 400 uplink beams each having 12 sub-bands, 4800dedicated demodulators would be required. Because the maximum capacityis much less than the 4800 potential communication sub-bands, however,many demodulators would be underutilized and, even at maximum footprinttraffic, many demodulators would be idle.

[0004] As a result of low utilization rates, a dedicated demodulatorarchitecture has the drawbacks of relatively high power consumption andundesirable added weight to the satellite.

[0005] The traffic of a beam varies with the demand, time-of-day, and/ormotion of the satellite (in the case of non-geosynchronous satellites).Thus, there exists a need for an uplink architecture with a pool ofdemodulators that can be assigned dynamically to the beams based ontheir needs. A scalable switch matrix provides reliable uplink signalprocessing, and reduces the amount of required hardware versus dedicateddemodulator architectures, thereby eliminating additional power, volume,mass, and complexity.

DISCLOSURE OF THE INVENTION

[0006] The present invention has several advantages over existingarchitectures. The present invention is a scalable switch matrix anddemodulator bank architecture for a satellite payload processor whereinthe demodulators are connected to the output ports of the switches andassigned optimally to the beams as the load on the uplink beams varies.Thus, a smaller number of demodulators are required to process theuplink signals. This results in a readily scalable architecture havinghigher utilization of the demodulators, smaller switch sizes, and ahigher efficiency and overall reliability.

[0007] These advantages are accomplished through the use of a highcapacity switch matrix for processing data from many uplink transmissionbeams wherein each of the transmission beams is capable of carrying anactive communication signal in any one of several sub-bands.

[0008] The switch matrix includes a first switch layer including one ormore switches, each having several inputs and outputs. Each of theswitch inputs are connected to receive one of the uplink transmissionbeams such that the total number of switch inputs is greater than orequal to the number of uplink transmission beams. The switch matrix alsoincludes a plurality of demodulators for retrieving data from the activecommunication sub-bands of the transmission beams. The total number ofdemodulators is limited to the maximum number of communication sub-bandswhich can be active at any one given time. This number is generally muchless than the number of sub-bands per beam times the number of uplinktransmission beams.

[0009] A second switch layer is connected between the first switch layerand the demodulators. The second switch layer includes groups of varyingnumbers of switches such that the output ports of the first switches areconnected to a varying number of demodulators. Thus, when a first switchreceives uplink transmission beams having many active communicationsub-bands, it routes the data traffic to an output port having acorresponding number of demodulators.

[0010] In another aspect of the invention, a tandem switch is configuredparallel to the first switch layer and is used to direct overflowtraffic to underutilized switches in the first switch layer. Thisarrangement of the switch matrix allows any of the uplink transmissionbeams to be connected to a time-varying number of demodulators. Otheradvantages of the invention will become apparent when viewed in light ofthe following detailed description and appended claims, and uponreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For a more complete understanding of this invention, referenceshould now be had to the embodiments illustrated in greater detail inthe accompanying drawings and described below by way of examples of theinvention. In the drawings:

[0012]FIG. 1 is a schematic representation of a scalable switch matrixin accordance with one embodiment of the present invention;

[0013]FIG. 1A is a table representing the input and output connectionsassociated with the first layer switches of FIG. 1; and

[0014]FIG. 2 is a schematic representation of a scalable switch matrixaccording to another embodiment of the present invention.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

[0015] Referring to FIG. 1, there is shown one embodiment of thescalable switch matrix and demodulator bank of the present invention. Asshown in FIG. 1, the switch matrix includes a first switch layer 10, asecond switch layer 12, and a plurality of demodulators 14. In thisexample, the switch matrix is configured to process a 400 beam uplinkpayload wherein the uplink beams are divided into 200 left and 200 rightpolarizations. Only the first beam 16 and the last beam 18 are shown,although it is to be understood that uplink transmission beams 2 through199 would be similarly connected to the switch matrix.

[0016] Since one polarization is typically sufficient to carry the dataload of a majority of uplink transmissions, a plurality of 2×2 switches20 and a 200×20 switch 22 are used to pick up the desired polarizationfor the load traffic cells, and direct both polarizations to the firstswitch layer 10, if necessary, for uplink beams with heavy data traffic.Thus, there are 200 uplink transmission beams connected directly to thefirst switch layer 10 by the 2×2 switches 20, and as many as 20additional uplink transmission beams can be connected to the firstswitch layer 10 by the 200×20 switch 22. This results in a total of 220potential inputs.

[0017] Alternatively, the 2×2 switches 20 and the 200×20 switch 22 couldbe eliminated and all of the uplink transmission beams could be directlyconnected to input ports of the switches within the first switch layer10 for a total of 400 potential inputs.

[0018] The first switch layer 10 includes ten 28×28 switches 24 which,in this case, are point-to-point switches. In this example, ten 28×28switches 24 are shown because of the need to accommodate 220 inputs fromthe 2×2 switches 20 and the 200×20 switch 22, as well as six inputs perswitch 24 received by the 60×60 tandem switch 26. of course, any numberof switches 24, including a single switch, could be used, and the sizeof the switch 24 could likewise be varied.

[0019] The tandem switch 26 is used to direct overflow traffic fromswitches 24 operating at full capacity to other switches 24 operating atless than full capacity as is known in the act.

[0020] Since each input transmission beam requires a variable number ofdemodulators to process the data traffic associated with the input beam,the output ports of the 28×28 switches 24 are connected to a varyingnumber of 8×4 switches 28 in the second switch layer 12. The table inFIG. 1A shows the relationship between the number of output switch portsin the 28×28 switches 24 and the corresponding number of 8×4 switches 28that those output ports are connected to. As shown in FIG. 1A, the firstoutput port is connected to 12, 8×4 switches 28; the next two outputports are connected to 10, 8×4 switches 28; the next two output portsare connected to eight, 8×4 switches 28; and so on. By changing therelationship of the output ports and the connections in the secondswitch layer, the traffic pattern that the switches 24 of the firstswitch layer can support can be altered.

[0021] Referring again to FIG. 1, the maximum number of 8×4 switches 28connected to any single output port of the 28×28 switches 24 is 12which, in this example, corresponds to the number of frequency channelsor sub-bands associated with each uplink transmission beam.

[0022] The demodulators 14 connected to a particular 8×4 switch 28 areall of the same type and operate at the same frequency band. Thedemodulators 14 connected to different 8×4 switches 28 of the same 28×28switch 24 operate at different frequency bands. The sum of thesefrequency bands covers the entire allocated frequency spectrum which, inthis case, is shown as 300 MHz. Once the demodulators 14 process thedata received in the uplink transmission beams, the data is passed topacket switch 30 for routing the packets and then modulation andtransmission on one or more downlink beams (the downlink modulators andtransmitter is not shown).

[0023] The total number of demodulators is a function of the maximumdata rate for the entire uplink footprint. Due to the satelliteprocessing power, among other things, the total footprint traffic isgenerally much less than the maximum beam capacity times the number ofuplink transmission beams. In the case of the switch shown in FIG. 1,the total number of demodulators is 480. This corresponds to fourdemodulators per sub-band, per input switch bank. This contrasts withthe 4800 demodulators which would be required in a dedicatedarchitecture for 400 transmission beams each having 12 sub-bands. Here,the maximum data rate is defined as the total number of sub-bands ineach transmission beam which could be active at any one time.

[0024] All of the switches shown in FIG. 1 can receive and implement thecommands from a central processor (not shown) to connect any input portto any output port. The central processor is aware of the footprinttraffic and the active sub-bands within each beam.

[0025] The tandem switch 26 is used to distribute the load to otherswitches 24 if the load on one or more of the 28×28 switches 24 exceedsthe demodulator availability at those switches. The central processordetermines which beams need to be off-loaded to other switches.

[0026] Referring to FIG. 2, there is shown a schematic diagram ofanother embodiment of the switch matrix of the present invention. Inthis example, again, the switch is intended to accommodate a 400 beamuplink payload having a 300 MHz spectrum divided into 12 frequency bandsor subchannels.

[0027] In this case, the first switch layer 40 includes 10 46×54switches 42. Each of the switches 42 has 46 inputs—40 per switch toaccommodate the 400 uplink transmission beams, and six per switch toroute overflow data traffic to the tandem switch 26. Similarly, eachswitch 42 has 54 outputs to accommodate four demodulators 44 persub-band, and six outputs for overflow data traffic to the tandem switch26.

[0028] Each demodulator 44 of a demodulator bank 46 is of the same typeand operates at the same frequency band. Each demodulator band 46connected to a different output port of the switches 42 and operates ata different frequency band. The sum of the frequency bands covers theentire allocated uplink frequency band spectrum, i.e. 300 MHz.

[0029] The switches 42 shown in FIG. 2, have broadcast or multi-castcapability as is known in the art. Thus, the switches 42 can multi-castan input beam to any number of demodulators attached to the output portsas needed to process the data traffic on the input transmission beam. Incontrast to the switches 24 of FIG. 1, switches 42 have increasedflexibility in adapting to various traffic patterns, but requireswitches with multi-cast capability and more cross-connections.

[0030] From the foregoing, it will be seen that there has been broughtto the art a new and improved switch matrix architecture which overcomesthe drawbacks associated with dedicated demodulator architectures. Whilethe invention has been described in connection with one or moreembodiments, it will be understood that the invention is not limited tothose embodiments. On the contrary, the invention covers allalternatives, modifications, and equivalents, as may be included withinthe spirit and scope of the appended claims. For example, referring toFIG. 1, all of the switches 20, 22, 24, and 28 could be of a differentnumber and size depending upon the number and characteristics of uplinkbeams and available technologies. Similarly, depending upon the uplinkbeam payload, the second switch layer 12 may be omitted (as in FIG. 2)or a third switch layer similar to the second may be required. Also, thedemodulators 14, 44 may be tunable demodulators rather than fixed at apredetermined frequency. It is, therefore, contemplated by the appendedclaims to cover any such modifications as incorporate those featureswhich constitute the essential features of these improvements within thetrue spirit and scope of the invention.

What is claimed is:
 1. A high-capacity switch matrix for processing datafrom a plurality of transmission beams wherein each of the transmissionbeams is adapted to carry an active communication signal in a pluralityof sub-bands, the switch matrix comprising: a first switch layerincluding a first switch having a plurality of input and output ports,each of said input ports connected to receive one of said plurality oftransmission beams and the total number of said input ports beinggreater than or equal to the plurality of transmission beams; aplurality of demodulators, each capable of demodulating a sub-band fromsaid active communication signals of said transmission beams; and asecond switch layer connected between said first switch layer and saiddemodulators, said second switch layer including a plurality of secondswitches each of said second switches having a plurality of input andoutput ports each of said input ports being connected to one of saidfirst switch output ports and each of said second switch output portsbeing connected to one of said plurality of demodulators such that atleast one output port of said first switch is connected to a differentnumber of demodulators through said plurality of second switches.
 2. Thehigh-capacity switch matrix of claim 1 wherein said first switch is apoint-to-point switch.
 3. The high-capacity switch matrix of claim 1wherein said first switch layer includes a plurality of first switchesand wherein the total number of said plurality of first switch inputports is greater than or equal to the plurality of transmission beams.4. The high-capacity switch matrix of claim 3 further comprising atandem switch having a plurality of input and output ports, said inputports being connected to at least one output of each of said pluralityof first switches and said outputs being connected to at least one inputof each of said plurality of first switches said tandem switch beingadapted to balance the load of active communication signals beingprocessed by each of said first switches.
 5. The high-capacity switchmatrix of claim 3 wherein at least one of said plurality of firstswitches is a point-to-multipoint switch.
 6. The high-capacity switchmatrix of claim 1 wherein said plurality of demodulators are arranged ina plurality of demodulator banks each of said demodulator banksoperating at a predetermined frequency sub-band of said transmissionbeams.
 7. The high-capacity switch matrix of claim 6 wherein saidplurality of second switches are arranged in groups, each of said groupsbeing connected to an output port of said first switch, at least one ofsaid groups comprising a plurality of second switches equal to thenumber of frequency sub-bands associated with said transmission beams.8. The high-capacity switch matrix of claim 1 wherein said plurality ofdemodulators are tunable.
 9. A multibeam uplink switch matrix for asatellite comprising: a first switch layer including at least onepoint-to-multipoint switch having a plurality of input and output portseach of said input ports connected to one beam of the multibeam uplinktransmission and wherein the total number of said inputs is greater thanor equal to the number of transmission beams; and a plurality ofdemodulator banks including at least one demodulator each of saiddemodulators capable of demodulating a sub-band from one of saidtransmission beams, at least one of each of said plurality ofdemodulator banks connected to each of said outputs of saidpoint-to-multipoint switch.
 10. The multibeam uplink switch matrix ofclaim 9 further comprising a tandem switch having a plurality of inputsand outputs, said inputs being connected to at least one output of eachof said point-to-multipoint switches and said outputs being connected toat least one of each of said inputs of said point-to-multipointswitches, said tandem switch being adapted to balance the load of activecommunication signals being processed by each of saidpoint-to-multipoint switches.
 11. The multibeam uplink switch matrix ofclaim 9 wherein each of said demodulator banks operates at apredetermined frequency sub-band of said transmission beams.
 12. Themultibeam uplink switch matrix of claim 9 wherein each of saiddemodulators is tunable.
 13. The multibeam uplink switch matrix of claim9 further comprising a second switch layer including at least one switchconnected between said first switch layer and said plurality ofdemodulator banks.
 14. The multibeam uplink switch matrix of claim 13wherein said second switch layer switch is a point-to-point switch. 15.The multibeam uplink switch matrix of claim 13 wherein said secondswitch layer switch is a point-to-multipoint switch.
 16. A switch matrixfor recovering data signals from a multibeam satellite uplinktransmission wherein each beam of said multibeam transmission includes aplurality of frequency channels capable of carrying an active datasignal, the switch matrix comprising: a first switch layer including atleast one switch having a predetermined number of inputs and outputs,said number of inputs being greater than or equal to the number oftransmission beams; and a predetermined number of demodulators, saidnumber of demodulators being less than or equal to the maximum number ofactive frequency channels at any given time wherein each of said switchoutputs are connected to at least one demodulator and at least one ofsaid switch output ports are connected to a different number ofdemodulators.
 17. The switch matrix of claim 16 wherein each of saiddemodulators are tunable.
 18. The switch matrix of claim 16 wherein saidat least one switch is a point-to-point switch.
 19. The switch matrix ofclaim 16 wherein said at least one switch is a point-to-multipointswitch.